The present invention relates to the structure of a superconducting magnetic levitation apparatus for running a superconductor with a floating state.
In a non-contact transport system no friction is generated on a running track, and thus high speed and dust-free transportation can be achieved. A linear motor of the magnetic levitation type is known as an example of a non-contact transport system. Specifically, a magnetic levitation railroad of the magnetic repulsion type has been developed with a view to transporting passengers at high speed and is required to generate a strong magnetic field for supporting a train itself and passengers. Thus, a superconducting magnet is used in the magnetic levitation railroad. While, in a place where dust is to be avoided, for example, in a hospital or semiconductor work, a magnetic levitation linear motor of the magnetic repulsion type or magnetic attraction type is used for dust-free transportation. In the dust-free transportation, it is not required to transport heavy goods, therefore an electromagnet consisting of normal conductor(s) is used. As mentioned above, various types of magnetic levitation linear motors have been used for various purposes. In any case, however, it is difficult to control a magnetic field for maintaining a floating state. Accordingly, a transport system using the linear motor becomes expensive.
A high-T.sub.c superconductor whose critical temperature is higher than the liquid nitrogen temperature, has been discovered in recent years. Thus, magnetic levitation and running which utilize the diamagnetism of a superconductor, can be realized by a combination of a magnet and a high-T.sub.c superconductor. This combination is entirely different from the transport system using the above-mentioned magnetic levitation linear motor, and makes possible inexpensive, dust-free non-contact transportation.
Examples of the magnetic levitation apparatus of the diamagnetic type using a high-T.sub.c superconductor will be explained below. In, for example, Nikkan Kogyo Shinbun, Nov. 25, 1987, a high-T.sub.c superconductor is disposed along a slope, to be used as a rail, a magnet is used as a floating body, and the floating body is moved in a horizontal direction by gravity.
In, for example, Shinbun, Mar. 28, 1989. The positional relationship between the high-T.sub.c superconductor and the magnet is reversed, that is, the superconductor is used as the floating body. As in the first example, the superconductor is moved along the slope by gravity.
Page 18 of the digests of the 12th annual conference on 1988 magnetics in Japan held on Sep. 30, 1988, proposes a superconductor which floats over a magnet, and follows the magnet when the magnet is moved on the ground in a horizontal direction.
In abstracts of 38th Meeting on Cryogenics of Japan held in 1987, an arrangement is proposed wherein a magnet floats over a plurality of stripe-shaped superconductors on the ground side, and is moved in a horizontal direction by controlling the superconducting state of each superconductor. That is, the transition between a superconducting state and a normal conducting state is used for driving force.
In JP-A-2-250305 a track having a uniform magnetic field in a running direction is formed of a lifting magnet, and a superconductor floating over the lifting magnet is moved in a horizontal direction by a varying magnetic field generated by the magnets for propulsion.
In the first and second mentioned examples, the moving speed and direction are determined by the slope. That is, no consideration is given as how the movement of the floating body in the horizontal direction is controlled. Further, in the third mentioned example, it is necessary to move the magnet, and the relative position of the floating superconductor for the magnet is kept unchanged. The first to third examples fail to show a satisfactory method of running a body maintained at a floating state. In the fourth example, it is difficult to control the repetition period of the transition between the superconducting state and the normal conducting state, that is, the running speed of the floating body, and moreover a strong driving force cannot be obtained. In the fifth example, also, no thoughtful consideration is not give to a method of driving the floating body made of a superconductor, and detailed explanation of the arrangement of propulsion magnets, the shape of each propulsion magnets and a method of exciting the propulsion for efficiently running the floating body is not found. For example, in an embodiment of the fifth example, the propulsion magnets are disposed on the side surface of the lifting magnet, and thus the center axis of each propulsion magnet is not perpendicular to the floating plane of the superconductor. Accordingly, the magnetic coupling between the propulsion magnets and the superconductor is weak. Further, the propulsion magnets are excited by a pulsive direct current so as to form a magnetic field gradient in a magnetic field which is generated by the lifting magnet and is uniform in a running direction, thereby moving the floating body to a position having a low magnetic potential. The above excitation method, however, cannot produce a strong driving force. Further, according to the above pulsive method, it is necessary to excite a driving magnet in synchronism with the movement of the floating body. It is difficult to excite the propulsion magnet at an appropriate time and to control the running of the floating body.
Further, in the fifth example, not much consideration is given to the shape of the lifting magnet. That is, when the lifting magnet is made up of a plurality of magnet pieces, the uniformity of magnetic field is disturbed at the connecting position of two magnet pieces, and thus it is difficult to obtain a uniform magnetic field all over the lifting magnet.
Additionally, in the fifth example, the stability of the superconductor in a lateral direction in a case where the superconductor runs over the track formed of the lifting magnet, that is, the guidance force for the superconductor is given by a magnetic flux which is generated by the lifting magnet, and enters into and is trapped by the superconductor. Accordingly, a strong guidance force cannot be obtained. Thus, when the superconductor runs over the track, the superconductor is unstable, that is, there arises a problem that the superconductor vibrates in a lateral direction or deviates from the track.